During drilling of an oil well, gas well, or other well, a casing comprising several segments arranged end-to-end is put into place on the walls of the borehole. The various segments are installed as drilling proceeds, the segments at the drilling bottom having to pass through those already installed.
To maintain the largest possible passage section, the drilling device can comprise an enlargement tool that is generally positioned above a head tool that is designed to dig the bottom of the slot, such as a drill bit, for example.
In a known way, an enlargement tool comprises a body whose cross-section is less than the diameter of the casing and that has a circular shape along a longitudinal axis that is merged with the axis of the drilling device. This body comprises at an upper end a connection to an upper rod of the drilling device and at a lower end a connection to a lower rod of the drilling device. It also comprises a central pipe to allow the passage of a fluid in the direction of the head tool.
The enlargement tool also comprises several arms that are mobile relative to the body between a retracted position in which they do not protrude relative to the body and an extended position in which they protrude relative to the body so that the rotation of the enlargement tool along the longitudinal axis causes the enlargement of the borehole.
Several kinematic options can be envisioned for changing the positions of the arms. According to a first kinematic option, the arms pivot relative to an axis of rotation that is perpendicular to the longitudinal axis, as illustrated by way of example by the document U.S. Pat. No. 7,401,666.
According to a second kinematic option, the arms move translationally relative to the body in a direction that is perpendicular to the longitudinal axis or inclined relative to said axis. The invention relates more specifically to this kinematic option that is described in particular in the documents U.S. Pat. No. 6,615,933 and U.S. Pat. No. 6,732,817.
The document U.S. Pat. No. 6,615,933 describes a kinematic option with arms that move translationally perpendicularly to the longitudinal axis, whereas the document U.S. Pat. No. 6,732,817 describes a kinematic option with arms that move translationally in a direction that is inclined relative to the longitudinal axis.
As a supplement to the kinematic option, different types of actuators exist to cause the movement of the arms from the retracted position to the extended position.
The invention also relates more specifically to tools comprising a piston guided into the body so as to move translationally in a longitudinal direction (parallel to the longitudinal axis) and that comprises at least one bearing surface in contact with the arms.